Field of the Invention
The present invention relates to a display device, and more particularly to an organic light emitting diode (OLED) display device and a method of driving the same.
Discussion of the Related Art
Research is being done on various flat panel display devices that are thin and light, and have low power consumption. For example, flat panel display devices are categorized into liquid crystal display (LCD) devices, plasma display panel (PDP) devices, OLED display devices, etc.
OLED display devices apply a data voltage (Vdata) having various levels to respective pixels to display different grayscale levels, thereby realizing an image. Thus, each pixel includes one or more capacitors, an OLED, and a driving transistor that functions as a current control element. In more detail, a current flowing in the OLED is controlled by the driving transistor, and the amount of a current flowing in the OLED is changed by the threshold voltage deviation of the driving transistor and various parameters, causing the luminance non-uniformity of a screen.
In addition, a threshold voltage deviation of a driving transistor occurs because a characteristic of the driving transistor is changed by a variable manufacturing process. To solve such a problem, a compensation circuit including a plurality of transistors and a capacitor is provided in each pixel so as to compensate for the threshold voltage deviation.
In particular, a plurality of control circuits for controlling a plurality of transistors such as a switching transistor and an emission control transistor are used, and for example, may include a scan signal, an emission control signal, etc. Because an emission control transistor driven by the emission control signal maintains a turn-on state for a long time, the emission control transistor is quickly deteriorated, causing a degradation in a quality of an image.
Moreover, when a threshold voltage of the driving transistor is negative, because it is unable to compensate for the negative threshold voltage, a level of a current flowing in an OLED is changed due to a deviation of the negative threshold voltage and a deviation of a low-level source voltage caused by an IR drop, causing a degradation in a quality of an image.